Voice signal processor

ABSTRACT

A signal output is taken out from the input stage or respective output stages of the signal characteristic processing means through a signal line selected by selecting means. In accordance with the taken signal, the level control signal generating means sets the output level of the audio output signal. Then, the output level setting means sets the output level of the audio output signal in accordance with the level control signal outputted by the level control signal generating means. Therefore, the switching noise due to switch signal lines by selecting means is prevented from entering into an audio output signal during the processing of the output level of the audio input signal.

TECHNICAL FIELD

The present invention relates to an audio signal processing apparatusand is suitably applicable to an audio input signal processingapparatus, such as an audio mixer, which controls the frequencycharacteristics and amplitudes of audio input signals when the audioinput signals are mixed, for example.

BACKGROUND ART

Conventionally, an audio mixer used for processing audio signals isequipped with a frequency processing section and an amplitude processingsection. The frequency processing section includes, for example, filterswhich controls the frequency characteristics of the inputted audiosignal. The amplitude processing section is generally referred to as afader or a dynamics which changes the amplitudes of the inputted audiosignal. Using these sections, a signal processing usually called aneffect processing is performed for the frequency characteristics andamplitudes of the inputted audio signal.

When performing the effect processing to change the frequencycharacteristics, two frequency processing operations such as rejectionof signal components by a filter and emphasis of signal components by anequalizer can be carried out in any order and the resulting frequencycharacteristics are the same.

If the audio signal inputted to the audio mixer has a signal level belowthe predetermined threshold, then performing the amplitude processing onthe audio signal using, for example, a compressor will not cause anychanges in the amplitude of the audio signal. In contrast, if anequalizer is placed at the former stage of the compressor so as toincrease the amplitude level of the signal in a predetermined frequencyrange to a level above the threshold and then an amplitude processing isperformed, the amplitude of the output signal varies in accordance withthat of the input signal. In other words, the characteristics of theoutput signals are different whether the equalizer performs theamplitude processing before the amplitude processing of the compressoror not. Therefore, when processing signals using the audio mixer, theamplitude processing is usually performed on input signal at a fixedstage taking into consideration the influence of the amplitudeprocessing.

In order to perform the amplitude processing on output signals having avariety of frequency characteristics and amplitude characteristics, ithas been proposed to perform the effect processing by adding a switcherwhich allows switching of the dynamics to desired stages of thefrequency processing and/or amplitude processing.

Referring to FIG. 3, in a mixer 1, an input trim 3 performs fineadjustment on an audio input signal S1 which is inputted from an inputterminal 2 thereto, and outputs the adjusted signal to a frequencyprocessing section 1A so as to perform the frequency processing for eachfrequency range.

The audio input signal S1, which is inputted via the input terminal 2,is sent out through a main signal line BL to a signal characteristicprocessing section which includes an amplitude processing section, suchas a fader 7, and the frequency processing section 1A. When the signalpasses through the frequency processing section 1A, a high-pass filter(HPF) 4 rejects a DC component of the signal and low frequency noisecomponents such as the sounds of wind, and a low-pass filter (LPF) 5rejects high frequency noise components. Further, an equalizer (EQ) 6emphasizes or rejects, for example, the voices (vocal) of human beingsand particular sounds of music instruments such as cymbals. After thefrequency processing performed by the respective stages of the frequencyprocessing section 1A, the fader 7 adjust the output level of the audiosignal and an output terminal 8 outputs the adjusted audio signal.

The mixer 1 includes selector switches SW1 to SW7 which connect anddisconnect between the input terminal 2, input trim 3, high-pass filter4, low-pass filter 5, equalizer 6, fader 7, and output terminal 8. Theselector switches SW1 to SW7 have their respective contacts connected toa dynamics 10 via matrix switchers 9A and 9B. The matrix switchers 9Aand 9B are switched so as to place the dynamics 10 between any adjacenttwo of input terminal 2, input trim 3, high-pass filter 4, low-passfilter 5, equalizer 6, fader 7, and output terminal 8.

FIG. 4(A) illustrates the selector switches SW (SW1 to SW7) whichselectively switch the main signal line BL that connects the inputterminal 2, input trim 3, fader 7, output terminal, and the respectivefrequency processing sections, each of the selector switches having fourcontacts 11A, 11B, 12A, and 12B. For example, when the dynamics 10 isselected, the contacts 11A is connected to the contact 12A and thecontact 11B is connected to the contact 12B as shown in FIG. 4(B). Atthe other stages where the dynamics 10 is not inserted, the contacts 11Aare connected to the contacts 11B and the contacts 12A are not connectedto the contacts 12B as shown in FIG. 4(C).

The dynamics 10 includes signal amplitude processing means such as alimiter and compressor that decreases an high output level, and anexpander and a gate that cuts cross talk appearing in the low outputlevel. Thus, using the matrix switchers 9A and 9B, the mixer 1 performsthe amplitude processing on the inputted audio input signal S1 based onan output signal from any one of the input terminal 2, input trim 3,high-pass filter 4, low-pass filter 5, equalizer 6, fader 7, and outputterminal 8, in order to output an output signal, that is, the mixer 1sets the output level.

Since the mixer 1 having the aforementioned configuration inserts thedynamics 10 into a desired stage of the main signal line BL by switchingthe selector switches SW1 to SW6, the apparatus suffers from a problemthat the audio input signal S1 is disconnected during a moment when theselector switches are switched and switching noise generated by theswitchers is mixed with the audio signal which is being transmitted overthe main signal line BL.

Also, the buses in matrix form in the matrix switchers 9A and 9B arecomplex in construction and costly accordingly. In order to prevent theaudio input signal S1 from being disappearing during the switchingoperation, the matrix switchers 9A and 9B provided in the mixer 1 shouldbe switched by a selection signal having a time constant. This makes theconstruction of the switcher more complex.

DISCLOSURE OF THE INVENTION

The present invention was made in view of the aforementioned drawbacks.The present invention provides an audio signal processing apparatuswhere switching noise is prevented from entering into the transmittedsignal when switching to selectively derive an output from a desiredstage of the signal characteristic processing section which performs thefrequency processing and/or the amplitude processing on the signal whensetting output level of the output signal.

In order to solve the aforementioned drawbacks, an apparatus accordingto the present invention has one or a plurality of signal characteristicprocessing means which receives an audio input signal and changes thefrequency characteristic and amplitude characteristic of the audiosignal; a plurality of signal lines which receive a signal output froman input stage of a signal characteristic processing means into whichthe audio signal enters, and from the output stage of one or a pluralityof signal characteristic processing means; a level control signalgenerating means which generates a control signal for determining anoutput level on the basis of the signal output received over the signallines selected, the output level being determined in accordance with theoutput of a selecting means which selects one of a plurality of signallines; and an output level setting means which adjusts the output levelon the basis of an output signal derived from a selected signalcharacteristic processing means, and outputs as an audio output signalfrom the apparatus, the output level being adjusted in accordance withthe level control signal. Thus, the apparatus of the invention canprevent switching noise from entering an audio output signal of theapparatus, the switching noise resulting from the switching operation ofthe signal lines when the level of the audio output signal of theapparatus is adjusted on the basis of the signal derived from the signalcharacteristic means over the selected signal lines.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram illustrating the configuration of anaudio signal processing apparatus according to the present invention;

FIG. 2 is a schematic diagram explaining an amplitude processing;

FIG. 3 is a schematic block diagram illustrating a conventional audiosignal processing apparatus; and

FIG. 4 is a schematic diagram explaining a selector switch.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described in detail withreference to the drawings.

(1) Configuration of Mixer

In FIG. 1 in which the same reference numerals are applied to partscorresponding to FIG. 3, reference numeral 20 generally denotes a mixerwhich processes an audio input signal S1 digitally processed. The inputtrim 3 receives the audio input signal S1 through a main signal line BLfrom an input terminal 2 and performs fine adjustment of the signallevel of the audio input signal S1. The frequency processing section 20Awhich includes a high-pass filter 4, a low-pass filter 5, and anequalizer 6 performs the frequency processing on the audio input signalS1. Thereafter, the level of the audio signal outputted from thefrequency processing section 20A is adjusted to a prescribed outputlevel by the fader 7 and is subsequently outputted to a gain reductionsection 21 which decreases the output level of the audio signal.

The outputs of the input terminal 2, input trim 3, high-pass filter 4,low-pass filter 5, equalizer 6, and fader 7 are connected to a switcher22 with the signal lines L1 to L6, respectively, and selectivelyconnected via the switcher 22 to a level control signal generatingsection 23.

In other words, the switcher 22 selectively connects the each signalline L1 to L6 to the level control signal generating section 23, therebysupplying the level control signal generating section 23 with audiosignal outputted from the input terminal 2, input trim 3, fader 7,output terminal 8, and the output stages in the frequency processingsection 20A.

In reality, signal lines are selected depending on the purposes of theaudio signal processing. When producing audio signals for, for example,broadcasting, the signal level is often controlled on the basis of anoutput signal from the signal line L6 such that the output level fromthe final stage meets the requirements of the broadcasting regulations.

When performing the audio signal processing for, for example, therecording of a compact disk (CD), only the required audio signal isderived after low noise components have been rejected and alevel-control is performed on the derived audio signal. Therefore, thesignal line L3 following the high-pass filter 5 may be selected.Conversely, the signal line L2 preceding the high-pass filter 5 may beselected so that the entire output level of the audio signal isdecreased and thereafter the signal may be subjected to the frequencyprocessing.

The level control signal generating section 23 produces a controlvoltage Vc as a control signal for setting an output level with respectto, on the basis of the audio signal derived through any one of thesignal lines L1 to L6 selectively switched by the switcher 22. Thecontrol voltage Vc is outputted to the gain reduction section 21composed of a DSP (Digital Signal Processor).

In this case, if the input level derived from the signal line is higherthan a prescribed lower threshold V_(th1) and lower than a predeterminedupper threshold V_(th2), the output level is set equal to the inputlevel. Therefore, the level control signal generating section 23 sets acontrol voltage Vc to 1.0.

If the input level derived from the signal line is lower than theprescribed lower threshold V_(th1) or higher than the prescribed upperthreshold V_(th2), the level control signal generating section 23computes a reduction amount of the output level, produces and outputsthe control voltage Vc according to the reduction amount to the gainreduction section 21. In this manner, the gain reduction section 21 canperform the level control according to the signal output of audio signalat the output of input terminal 2, input trim 3, fader 7, outputterminal 8, and each stage of the frequency processing section 20A.

For this purpose, the lower threshold V_(th1) and upper thresholdV_(th2) are preset to the level control signal generating section 23 fora specific input level on the basis of an input-output level curve(amplitude characteristic) (FIG. 2) of an output signal with respect toan input signal. Further, a desired reduction amount is preset for inputsignals which are lower than the threshold V_(th1) or higher than thethreshold V_(th2). The input-output level curve shows that the outputlevel is decreased if the input level is lower than the thresholdV_(th1), thereby decreasing noise level to effectively emphasize thenecessary sounds, and the output level is decreased if the input levelis higher than the threshold V_(th2), thereby preventing the maximumamplitude of the audio input signal from increasing to a level at whichthe mixer 20 can not normally process the signal.

The gain reduction section 21 multiplies the audio input signal S1 inputthereto by the control voltage Vc output from the level control signalgenerating section 23, thereby setting the output level of the audiosignal. In this case, the control signal produced by the level controlsignal generating section 23 is the only factor that determines theamplitude processing. Therefore, the gain reduction section 21 may beplaced separately from the level control signal generating section 23but connected remotely thereto, thereby implementing a simple circuitconfiguration as well as saving manufacturing costs.

The level control signal generating section 23 computes a reductionamount in accordance with the input level of the output signal derivedover the signal lines L1-L6. The gain reduction section 21 performs theamplitude processing on the audio input signal in accordance with thecomputed reduction amount. The resulting audio input signal S2 is outputvia output terminal 8.

(2) The Operation of the Embodiment

With the aforementioned construction, the input trim 3 performs the fineadjustment of signal level of the audio input signal S1 input via theinput terminal 2, and the frequency processing section 20A whichincludes the high-pass filter 4 and low-pass filter 5, and equalizer 6performs the frequency processing on the audio input signal S1. Theaudio signal that has been subjected to the frequency processing iscontrolled by the fader 7 to a predetermined output level before it isoutput to the gain reduction section 21.

When the switcher 22 is switched to connect the signal line L1 to thelevel control signal generating section 23, the signal is directed fromthe input terminal 2 to the level control signal generating section 23.Likewise, the switcher 22 is switched to direct audio signals at therespective signal lines L2 to L6 to the level control signal generatingsection 23. That is, the switcher 22 is switched to selectively connectone of the signal lines L2-L6 to the level control signal generatingsection 23, so that the output signal having been subjected either tothe level control or to the frequency processing is selected from theinput trim 3, fader 7, or a corresponding one output stage in thefrequency processing section 20A. The selected output is directed to thelevel control signal generating section 23.

Incidentally, the switcher 22 is of simple construction just enough forswitching the lines L1 to L6 to selectively connect to the level controlsignal generating section 23.

In this manner, the level control signal generating section 23 canreceive the output signals from the respective stages, i.e., outputsignals that have been subjected to the frequency processing at therespective stages of the frequency processing section 20A or that havebeen subjected to the amplitude processing by the input trim 3 or fader7. Using these output signals, a reduction amount can be applied to thesignal output in accordance with the frequency processing and/oramplitude processing. When selectively receiving the output signals fromthe respective stages, the main signal line BL is not switched by theswitcher and only the audio signal as information is output to the levelcontrol signal generating section 23. This can prevent switching noisefrom entering the audio input signal which is subjected to the frequencyprocessing.

The level control signal generating section 23 outputs the controlvoltage Vc to the gain reduction section 21, the control voltage Vcbeing in accordance with the reduction amount. Thus, the gain reductionsection 21 multiplies the audio input signal transmitted over the mainsignal line BL along the while being subjected to the frequencyprocessing by the control voltage Vc produced by the level controlsignal generating section 23, thereby outputting to the output terminal8 the audio signal S2 which has been subjected to the amplitudeprocessing so that the output level is adjusted in accordance with theresult of the frequency processing.

(3) Advantages of the Embodiment

With the aforementioned construction, the switcher 22 selects one of thesignal lines L1 to L6 to direct the audio output signal, which has beensubjected to a predetermined frequency processing at the respectivestages of the frequency processing section 20A, to the level controlsignal generating section 23. In accordance with the output signal fromthe selected stage at which the audio signal has been subjected to thefrequency processing, the level control signal generating section 23produces the control voltage Vc. Then, the gain reduction section 21multiplies the control voltage Vc by the audio input signal, therebyperforming the amplitude processing on the audio input signal S1 inaccordance with the signal output of the corresponding stage of thefrequency processing section 20A.

The gain reduction section 21 performs the amplitude processing bymultiplying the audio signal by the control voltage Vc after the audiosignal has been subjected to the frequency processing. Therefore, thesignal lines are not subjected to the switching operation, therebyeliminating the chance of switching noise entering the audio signalwhich is being transmitted over the main signal line BL.

Moreover, since there is no need that the switcher 22 switches the audioinput signal so as to cause the audio signal to be directly subjected tothe amplitude processing, the switcher 22 can be of simple constructionwhich reduces overall part costs of the mixer 20.

(4) Other Embodiments

Note that, in the aforementioned embodiment, the mixer 20 for a digitalsignal processing is provided with the gain reduction section 21composed of a DSP. However, the present invention is not limited theretoand a VCA (Voltage Controlled Amplifier) composed of OP amps may be usedto decrease the output level of the analog signal. In this case, inorder to lower an output level with respect to an input signal by 6[dB], a control voltage of 2.5 [V] can be supplied if the referencelevel of the VCA is 5 [V]. Thereby, the same advantages as theaforementioned embodiment can be obtained.

Further, in the aforementioned embodiment, the signal characteristicprocessing section is composed of a plurality of frequency processingsections and an amplitude processing section such as a fader. However,the present invention is not limited thereto and an apparatus can have asingle frequency processing section or a single amplitude section. Insuch a case, signal lines may be provided both on the input side and onthe output side of the frequency processing section, so that thefrequency processing section can be selectively connected to the levelcontrol signal generating section 23. This configuration provides thesame advantage as the aforementioned embodiment.

Further, in the aforementioned embodiment, an effect processing isperformed on the audio input signal S1 to be inputted to the mixer 20.However, the present invention is not limited thereto and an effectprocessing can be performed on an output signal after mixing signalswith the mixer.

In the aforementioned embodiment, an effect processing operation isperformed by the mixer 20 as an audio signal processing apparatus.However, the present invention is not limited thereto and be applied toapparatuses such as an echo apparatus in which an effect processing isusually performed by applying a frequency processing and an amplitudeprocessing.

Further, in the aforementioned embodiment the gain reduction section 21is provided at the end of the mixer 20. However, the present inventionis not limited thereto and the gain reduction section 21 can be placedat the end of the signal lines over which a desired output signal isderived.

Further, in the aforementioned embodiment, the level control signalgenerating section 23 is in the form of hardware. However, the presentinvention is not limited thereto and a level control signal can beproduced by software. It may be possible to select the signal outputfrom the signal lines L1 to L6 with software.

Furthermore, in the aforementioned embodiment, the reduction of outputlevel is performed by the gain reduction section 21 in accordance withthe control voltage Vc. However, the present invention is not limitedthereto and in the case where a wide dynamic range is not achievedduring recording, the frequency processing and amplitude processing canbe performed with the audio input signal maintained at a constant leveland the processed signal is recorded on a magnetic tape or the like, andwhen reproducing such a signal, the signal level of the reproduced audiosignal can be expanded to the signal level of the original audio inputsignal.

According to the present invention described above, selecting meansselects a signal lines to take out a signal from the input stage of thesignal characteristic processing means to which an audio input signal issupplied or the respective output stages of the signal characteristicprocessing means. Then, level control signal generating means produces alevel control signal for determining an output level of an audio signal,on the basis of the taken signal. Further, output level setting meanssets the output level of the audio input signal in accordance with thelevel control signal. Therefore, an audio signal processing apparatushaving a simple construction can be realized, in which switching noisedue to switching the signal lines by the selecting means is preventedfrom inserting into an audio output signal when controlling an outputlevel with respect to an audio input signal.

INDUSTRIAL APPLICABILITY

In the present invention, an audio signal processing apparatus, such asan audio mixer of a sound making equipment, can be utilized for anamplitude processing of an echo equipment and at the time of recording.

What is claimed is:
 1. An audio signal processing apparatus forcontrolling a frequency and an amplitude of an audio input signal andoutputting the signal as an audio output signal, comprising: one or aplurality of signal characteristic processing means for receiving saidaudio input signal and changing a frequency characteristic and anamplitude characteristic of said audio input signal; a plurality ofsignal lines for taking out signal outputs from an input stage of saidsignal characteristic processing means for said audio input signal andfrom an output stage of said one or plurality of signal characteristicprocessing means; selecting means for selecting one of said plurality ofsignal lines; level control signal generating means for generating acontrol signal for determining an output level of said signal outputobtained through a selected signal line based on the output of saidselecting means; and output level setting means for adjusting a level ofan output of said signal characteristic processing means in accordancewith the level control signal and outputting the output as an audiooutput signal.
 2. The audio signal processing apparatus according toclaim 1, wherein said level control signal generating means computes areduction amount for a level of said signal output which is higher thanan upper threshold or lower than a lower threshold, based on aprescribed input/output level characteristic, to produce said controlsignal in accordance with the reduction amount.